possible deadlock in f_midi_transmit

[Rondreis]

Hello,

When fuzzing the Linux kernel driver v6.0-rc4, the following crash was
triggered.

HEAD commit: 7e18e42e4b280c85b76967a9106a13ca61c16179
git tree: upstream

kernel config: https://pastebin.com/raw/xtrgsXP3
C reproducer: https://pastebin.com/raw/C1xYEf7Q
console output: https://pastebin.com/raw/3RLhvQHE

Basically, in the c reproducer, we use the gadget module to emulate
attaching a USB device(vendor id: 0x403, product id: 0xff3d, with the
midi function) and executing some simple sequence of system calls.
To reproduce this crash, we utilize a third-party library to emulate
the attaching process: https://github.com/linux-usb-gadgets/libusbgx.
Just clone this repository, install it, and compile the c
reproducer with ``` gcc crash.c -lusbgx -lconfig -o crash ``` will do
the trick.

I would appreciate it if you have any idea how to solve this bug.

The crash report is as follows:


============================================
WARNING: possible recursive locking detected
6.0.0-rc4+ #20 Not tainted
--------------------------------------------
kworker/0:1H/9 is trying to acquire lock:
ffff888057ed9228 (&midi->transmit_lock){....}-{2:2}, at:
f_midi_transmit+0x18c/0x1460 drivers/usb/gadget/function/f_midi.c:683

but task is already holding lock:
ffff888057ed9228 (&midi->transmit_lock){....}-{2:2}, at:
f_midi_transmit+0x18c/0x1460 drivers/usb/gadget/function/f_midi.c:683

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&midi->transmit_lock);
  lock(&midi->transmit_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by kworker/0:1H/9:
 #0: ffff888011c65138 ((wq_completion)events_highpri){+.+.}-{0:0}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: ffff888011c65138 ((wq_completion)events_highpri){+.+.}-{0:0}, at:
arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline]
 #0: ffff888011c65138 ((wq_completion)events_highpri){+.+.}-{0:0}, at:
atomic_long_set include/linux/atomic/atomic-instrumented.h:1280
[inline]
 #0: ffff888011c65138 ((wq_completion)events_highpri){+.+.}-{0:0}, at:
set_work_data kernel/workqueue.c:636 [inline]
 #0: ffff888011c65138 ((wq_completion)events_highpri){+.+.}-{0:0}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:663 [inline]
 #0: ffff888011c65138 ((wq_completion)events_highpri){+.+.}-{0:0}, at:
process_one_work+0x8b0/0x1650 kernel/workqueue.c:2260
 #1: ffffc900003afdb0 ((work_completion)(&midi->work)){+.+.}-{0:0},
at: process_one_work+0x8e4/0x1650 kernel/workqueue.c:2264
 #2: ffff888057ed9228 (&midi->transmit_lock){....}-{2:2}, at:
f_midi_transmit+0x18c/0x1460 drivers/usb/gadget/function/f_midi.c:683

stack backtrace:
CPU: 0 PID: 9 Comm: kworker/0:1H Not tainted 6.0.0-rc4+ #20
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
1.13.0-1ubuntu1.1 04/01/2014
Workqueue: events_highpri f_midi_in_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2988 [inline]
 check_deadlock kernel/locking/lockdep.c:3031 [inline]
 validate_chain kernel/locking/lockdep.c:3816 [inline]
 __lock_acquire.cold+0x152/0x3c3 kernel/locking/lockdep.c:5053
 lock_acquire kernel/locking/lockdep.c:5666 [inline]
 lock_acquire+0x1ab/0x580 kernel/locking/lockdep.c:5631
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x39/0x50 kernel/locking/spinlock.c:162
 f_midi_transmit+0x18c/0x1460 drivers/usb/gadget/function/f_midi.c:683
 f_midi_complete+0x1bb/0x480 drivers/usb/gadget/function/f_midi.c:285
 dummy_queue+0x84a/0xb20 drivers/usb/gadget/udc/dummy_hcd.c:736
 usb_ep_queue+0xe8/0x3b0 drivers/usb/gadget/udc/core.c:288
 f_midi_do_transmit drivers/usb/gadget/function/f_midi.c:658 [inline]
 f_midi_transmit+0x7e4/0x1460 drivers/usb/gadget/function/f_midi.c:686
 process_one_work+0x9c7/0x1650 kernel/workqueue.c:2289
 worker_thread+0x623/0x1070 kernel/workqueue.c:2436
 kthread+0x2e9/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
 </TASK>